Here's a very detailed set of instructions for a quick introduction to photographic depth of field. This demonstration works the same way for film or digital.

1. 3/14/2009
Depth of field demo
©2009 Len Cook
Basic scene
Depth of field is the range of acceptable
sharpness in a photograph of a scene.
h i ht hf
Depth of field changes when the photographer
changes aperture.
Depth of field is greater when the photographer
uses small apertures.
uses small apertures
Depth of field is less when the photographer
uses large apertures.
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Basic scene
• Changes in depth of field are easiest to see when
these items are in use:
these items are in use:
A camera
–
A lens
–
An object or person that is the subject
–
An object or person closer to the camera than the
–
subject, but still in the picture.
– An object or person farther from the camera than the
subject, but still in the picture.
– Enough light to shoot a photo at f/22
Basic scene
Example:
Item farther
Item closer
Item closer Subject
than the
than the
subject from
subject to the
Camera Lens the camera
camera
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3. 3/14/2009
View through the camera
• Focus on the subject at f/2.8 in this example.
f/2.8 is the largest aperture on the lens in this example.
Viewing aperture
• All modern cameras keep the lens aperture
fully open for focusing.
fully open for focusing
• The diaphragm stops down to the working
aperture ONLY during the exposure while the
shutter is open.
• SOME cameras have a depth‐of‐field preview.
• DOF preview allows the photographer to view
through the lens at the aperture the photo
will use.
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Set the aperture to f/2.8
• Take a picture and it will look like this:
Item closer
Item farther
than the
than the
subject to the
subject from
camera is out
the camera is
of focus.
out of focus.
You must use a shutter speed appropriate to f/2.8! Take the picture NOW.
Change the aperture
• Now you must change the aperture to the
smallest available aperture on your camera/lens
smallest available aperture on your camera/lens
combination, f/22 in this example.
• You must also change the shutter speed.
• Because you are going from f/2.8 to f/22 you will
reduce the light hitting the film or sensor by 6
stops. That is a very big reduction.
• You must increase the exposure time by 6 stops.
That is a very big increase.
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5. 3/14/2009
View the scene again
• Focus on the SAME SUBJECT!
Keep the camera at the same distance as the first picture.
Focus on the same subject as the first picture.
View through the camera
• Focus on the subject, aperture at f/22.
Even with the aperture set at f/22, the view looks the same as it did at f/2.8.
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Full aperture viewing
• You changed the aperture to f/22 but the view
through the camera looks the same.
th h th l k th
• All modern cameras keep the lens aperture
fully open for focusing.
• The diaphragm stops down to the working
aperture ONLY during the exposure while the
aperture ONLY during the exposure while the
shutter is open.
Depth‐of‐field preview
• SOME cameras have a depth‐of‐field preview.
• DOF preview allows the photographer to view
through the lens at the aperture the photo
will use.
• Sometimes DOF preview is a button.
Sometimes it is a lever.
Sometimes it is a lever
• DOF preview control (button or lever) may be
on the lens or may be on the camera.
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7. 3/14/2009
Preview depth‐of‐field
• If you have it, use it and the viewfinder will
look like this:
DOF preview may make the viewfinder VERY dark if a small aperture is set.
Depth‐of‐field greatly expanded
• Take a picture at f/22 and it will look like this:
Item closer
Item farther
than the
than the
subject to the
subject from
camera is
the camera is
much sharper.
much sharper.
You must use a shutter speed appropriate to f/22!
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8. 3/14/2009
Now you try it
• Repeat this process with subjects of your own.
• Try different subjects.
• The three items or persons in the photo can
be different. They do not have to be three of
the same thing, like juice cans.
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